1. Field of the Disclosure
The present disclosure relates to a liquid crystal display device. The present disclosure also relates to a backlight unit where a thickness is reduced by changing the number and the structure of housings and a liquid crystal display device including the backlight unit.
2. Discussion of the Related Art
Since the liquid crystal display (LCD) device has advantages such as high contrast ratio and superiority in displaying a moving image, the LCD device has been used for a monitor of a computer or a television. The LCD device displays an image by using optical anisotropy and polarization properties of liquid crystal molecules.
The LCD device includes two substrates having a pixel electrode and a common electrode, respectively, and a liquid crystal layer between the two substrates. In the LCD device, an alignment direction of liquid crystal molecules of the liquid crystal layer is determined according to an electric field between the pixel electrode and the common electrode and transmittance difference is obtained in the liquid crystal layer by the alignment direction.
However, since the LCD device is a non-emissive type display device, an additional light source is required to display an image by transmittance difference. Accordingly, a backlight unit including a light source is disposed under the liquid crystal panel. For example, one of a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL) and a light emitting diode (LED) may be used as the light source of the backlight unit. Among various light sources, the LED has been widely used as the light source for its various features such as a small size, a low power consumption and a high reliability.
FIG. 1A is an exploded perspective view showing a liquid crystal display device according to the related art, and FIG. 1B is a cross-sectional view taken along a ling IB-IB of FIG. 1A.
In FIGS. 1A and 1B, a liquid crystal display (LCD) device includes a liquid crystal panel 110, a backlight unit 120, a main frame 130, a top frame 140 and a bottom frame 150. The liquid crystal panel 110 for displaying an image includes first and second substrates 112 and 114 facing and spaced apart from each other and a liquid crystal layer (not shown) between the first and second substrates 112 and 114. First and second polarizing plates 19a and 19b are formed on outer surfaces of the first and second substrates 112 and 114, respectively.
The backlight unit 120 for supplying a light is disposed under the liquid crystal panel 110. The backlight unit 120 includes a light emitting diode (LED) assembly 129 along at least one side of the main frame 130, a reflecting plate 125 of a white color or a silver color on the bottom frame 150, a light guide plate 123 on the reflecting plate 125 and an optical sheet 121 on the light guide plate 123. The LED assembly 129 is disposed at side of the light guide plate 123 and includes an LED printed circuit board (PCB) 129a and a plurality of LED packages 129b mounted on the LED PCB 129a. 
The main frame 130 having a rectangular ring shape wraps side surfaces of the liquid crystal panel 110 and the backlight unit 120. In addition, the top frame 140 covers front edge portions of the liquid crystal panel 110, and the bottom frame 150 covers a bottom surface of the backlight unit 120. Accordingly, the liquid crystal panel 110 and the backlight unit 120 are modularized by combining the top frame 140 and the bottom frame 150 with the main frame 130.
FIG. 2A is a perspective view showing an LED package according to the related art and FIG. 2B is a perspective view showing an LED assembly according to the related art.
In FIG. 2A, an LED package 129b includes a case 30 having a body 32 and first to fourth sidewalls 33, 35, 37 and 39 protruding from the body 32, an LED chip 42 disposed in a space surrounded by the first to fourth sidewalls 33, 35, 37 and 39, and first and second electrode leads 44 and 46 exposed outside the case 30. Although not shown, the first and second electrode leads 44 and 46 are connected to the LED chip 42 through a wire, and a fluorescent material is formed in the space surrounded by the first to fourth sidewalls 33, 35, 37 and 39 to cover the LED chip 42.
In FIG. 2B, the LED package 129b is mounted on an LED PCB 129a such that the first sidewall 33 of the LED package 129b is attached to a top surface of the LED PCB 129a. Accordingly, an emitting surface 40 facing the LED chip 42 is disposed to be perpendicular to the top surface of the LED PCB 129a, and the LED package 129b emits a light along a direction parallel to the top surface of the LED PCB 129a. The LED assembly 129 where the light is emitted from the LED package 129b along a direction parallel to a top surface of the LED PCB 129a may be referred to as a side-view type.
As the LCD device has been widely used for a notebook and a smartbook, a demand for reduction in thickness of the backlight unit 120 of the LCD device increases. Since each of the reflecting plate 125 and the optical sheet 121 has a relatively small thickness, a thickness of the backlight unit 120 may be determined by a thickness of the LED assembly 129 and a thickness of the light guide plate 123.
Although a research for reducing a thickness of the LED package 129b of the LED assembly 129 has been performed, there exists a limit to reduction of a thickness of the LED package 129b. A first thickness t1 of the LED package 129b is a sum of a thickness of the first sidewall 33, a thickness of the emitting surface 40 and a thickness of the second sidewall 35. Since the first and second sidewalls 33 and 35 should constitute the case 30, there is a limit to reduction of the thickness of the first and second sidewalls 33 and 35. In addition, when the thickness of the emitting surface 40 is reduced, a luminous flux of the LED package 129b is also reduced. Since the LED package 129b has a minimum luminous flux, there is a limit to reduction of the thickness of the emitting surface 40. Accordingly, there exists a limit to reduction of a thickness of the backlight unit 120 due to reduction of the thickness of the LED package 129b. 
Further, since the LED package for a top-view type LED assembly is used for the side-view type LED assembly 129 by rotating the case 30, the LED package 129b includes the unnecessary first sidewall 33. As a result, the first sidewall 33 causes increase of the thickness of the backlight unit 120.
FIG. 3A is a perspective view showing a direction of a light from an LED assembly according to the related art and FIG. 3B is a plan view showing a distribution and a path of a light from an LED assembly according to the related art.
In FIGS. 3A and 3B, since the LED chip 42 is disposed in the case 30 to face an incident surface of the light guide plate 123 (of FIG. 1), the first to fourth sidewalls 33, 35, 37 and 39 are required for effectively reflecting a light L from the LED chip 42 toward the incident surface of the light guide plate 123 by a bottom surface 48 and a side surface 49. Since the case 30 including the first to fourth sidewalls 33, 35, 37 and 39 is fabricated through a molding method, fabrication process for the LED package 129b is complicated and fabrication cost for the LED package 129b increases.
Further, since the light L is radially emitted from the LED package 129b, the LED package 129b is disposed to be separated from the light guide plate 123 by a relatively short distance. As a result, the light from adjacent two LED packages 129b overlap to form a hot spot HS, and the hot spot HS degrades uniformity in luminance of the backlight unit 120.